SPN 654 FMI 11: Meaning and Fix
SPN 654 FMI 11 indicates the ECM has detected an anomaly on the fuel injector circuit for cylinder 4 but cannot determine the specific failure mode. This code often appears after a forced DPF regeneration or an ECM software update when injector trim values are reset. Technicians may find it alongside cylinder contribution faults, requiring careful analysis of wiring, connector pin fretting, and injector solenoid resistance values per SAE J1939-71.
Common Symptoms
- Rough Idle: Cylinder 4 misfire causes uneven engine rotation at low RPM, noticeable as vibration.
- Power Loss: ECM reduces fuel delivery to protect the injector, resulting in noticeable torque reduction under load.
- Increased Smoke: Unburned fuel from cylinder 4 produces white or gray exhaust smoke during cold starts.
- Hard Starting: Extended cranking time due to insufficient fuel atomization from the faulty injector circuit.
Probable Causes
- Open Injector Circuit: Broken wire or high resistance in the cylinder 4 injector harness, common after engine vibration.
- ECM Output Driver Damage: Internal ECM failure on the injector driver channel for cylinder 4, often from voltage spikes.
- Injector Solenoid Failure: Short or open within the injector solenoid coil, typically found after high-mileage operation.
- Connector Corrosion: Moisture ingress at the injector or ECM connector causing intermittent signal loss and FMI 11.
Advanced Technical Analysis
The ECM uses a dedicated high-side driver and low-side sense circuit to monitor injector solenoid current. For SPN 654 FMI 11, the microcontroller detects an invalid current profile during the pull-in or hold phase but cannot distinguish between an open, short, or mechanical stuck condition. The diagnostic algorithm compares the measured current against a calibrated envelope; any deviation outside 10-15% triggers the unknown root cause code.
Electrical analysis reveals that the ECM debouncing timer typically waits 0.5 to 2 seconds before setting FMI 11. A common scenario is intermittent connector fretting corrosion on the cylinder 4 pin at the ECM 120-pin connector. This creates a high-resistance path that fluctuates with engine temperature, passing the debounce test intermittently but eventually failing the continuous monitoring routine.
When SPN 654 FMI 11 activates, the ECM enters a safety fallback mode that derates engine torque by 25-40% and disables cylinder 4 fuel delivery. The engine control module also increments a fault counter; after three consecutive ignition cycles with the fault present, it locks the injector circuit and requires a diagnostic tool to clear the permanent fault memory per ISO 14229.
Long-term prevention involves inspecting injector harness routing for chafing near the valve cover and applying dielectric grease to connector seals. In workshops, this code frequently follows an ECM replacement where the injector trim files were not reprogrammed, causing the ECM to misread normal solenoid resistance as a fault. Always perform a injector electrical test using a breakout box before replacing components.
Step-by-Step Troubleshooting Guide
- Visual Inspection: Check cylinder 4 injector connector and ECM harness for corrosion, bent pins, or chafed wires.
- Resistance Measurement: Measure injector solenoid resistance between 0.5-2.0 ohms; compare to cylinder 3 and 5.
- ECM Output Test: Use a breakout box to verify ECM injector driver voltage during cranking with an oscilloscope.
- Injector Swap: Swap cylinder 4 injector with cylinder 6; if fault moves, replace the injector.